1. Field of the Invention
The present invention relates to a multi-layer printed circuit board, and more particularly, to a multi-layer printed circuit board having a plurality of bump connection pads for mounting a Ball Grid Array Packaging type semiconductor component, and its fabrication method. The present invention also relates to a printed circuit board having a thin printed circuit board compared to that of conventional art and which is capable of solving a problem of defective attachment of a bump due to a void in a blind via hole (referred to as xe2x80x98BVHxe2x80x99, hereinafter).
2. Description of the Background Art
FIG. 1 is a sectional view of a multi-layer printed circuit board in accordance with the conventional art.
As shown in the drawing, a plurality of resin layers 3a and 3b are stacked by a built-up method, and circuit patterns 5a, 5b and 5c made of metal thin layer are formed on each resin layer 3a and 3b. 
A blind via hole 7b is formed penetrating the resin layer to connect the upper circuit pattern 5c and the lower circuit pattern 5a. The blind via hole 7b is formed having a reversed conical shape wherein the diameter of the entrance is greater than that of the bottom. The entrance of the upper via hole 7b and the lower via hole 7a is positioned in the same direction (the upward direction in FIG. 1).
Plated layers 9a and 9b are formed at the inner side of the blind via holes 7a and 7b, respectively. The plated layer 9a, 9b are also extendedly formed on the upper surface of the upper circuit pattern 5c and the lower circuit pattern 5a. Thus, the upper circuit pattern 5c and the lower circuit pattern 5a are electrically connected by the plated layers 9a, 9b. 
An inner lead bump 11 for electrical connection with a semiconductor chip component (now shown) is attached at the upper portion of the plated layer 9b on the upper surface of the blind via hole 7b. 
A solder resist layer 12 covers the upper surface of the plated layer 9b and the resin layer 3b except for the portions where the inner lead bump 11 is attached. That is, in the conventional multi-layer printed circuit board of FIG. 1, the inner lead bump 11 is attached in the blind via hole.
A method for fabricating the above described printed circuit board will now be explained.
First, a cooper clad laminate (CCL) is prepared wherein an upper metal thin plate 4a and a lower metal thin plate 4b are coated on both surfaces of the lower resin layer 3a. 
The upper metal thin plate 4a and the lower resin layer 3a are etched to form a lower blind via hole 7a. The lower plated layer 9a is formed at the side wall face and the bottom surface of the lower blind via hole 7a to electrically connect the upper and the lower metal thin plates 4a, 4b. 
Thereafter, the upper metal thin plate 4a and the lower plated layer 9a are patterned to form the lower circuit pattern 5a. 
Next, the resin layer 3b and a metal film 4c are formed at the upper surface of the lower plated layer 9a and the lower resin layer 3a. 
And then, the metal film 4c and the upper resin layer 3b are partially etched to form the upper blind via hole 7b. At this time, the upper surface of the lower circuit pattern 5a is exposed through the upper blind via hole 7b. 
And, the upper plated layer 9b is formed at the upper surface of the metal film 4c, at the inner wall face of the upper blind via hole 7b and at the upper surface of the lower plated layer 9a exposed at the bottom of the upper blind via hole 7b. 
Then, the upper plated layer 9b and the metal film 4c are patterned. The patterned metal film 4c becomes the upper circuit pattern 5c. The upper circuit pattern 5c and the lower plated layer 9a are electrically connected by the upper plated layer 9b. 
Next, the solder resist layer 12 is formed at the upper surface of the upper plated layer 9b and at the exposed upper resin layer 3b except for the inside of the upper blind via hole 7b. The upper surface of the upper plated layer 9b, which is exposed by not being covered with the solder resist layer 11, is a pad for attaching a bump for mounting a chip component.
And then, the solder bump 13 is attached at the upper surface of the upper plated layer 9b within the upper blind via hole 7a, that is, at the pad.
However, the printed circuit board fabricated according to the conventional method has the following problems.
For example, first, since the bump 13 is formed at the upper portion of the upper blind via hole 7b, the air in the upper blind via hole 7b is not discharged externally, forming an air void 14, or the air flows into the bump 13 and remains there. Then, due to the heat generated in mounting a chip component on the printed circuit board or from the intense heat generated from use of its product, the blind via hole or the air void of the bump swells to generate a crack to the printed circuit board around the bump or to deteriorate the attachment state of the chip components, resulting in damage to the packaging state of the chip components of the printed circuit board.
Secondly, in an effort to solve the problem, a Japanese Patent Laid Open No. 10-284846 discloses a method in which, for mounting the bump, the pad is extendedly designed in the vicinity of the blind via hole, avoiding the blind via hole. In this case, however, a problem arise in that the printed circuit board increases in size.
Thirdly, in a flip chip fabricating process, when an under filler is filled between the chip and the printed circuit board to correct a difference in the heat expansion between the chip mounted on the printed circuit board and the printed circuit board, the under filler is not completely filled in the blind via hole 7, causing a problem in that the printed circuit board is deformed due to thermal impact.
Lastly, in the case of forming a flexible printed circuit board, if the resin layer is too thin, it is inconvenient to handle it during the fabricating process, degrading yield rate. A solution to this problem is to forming the resin thick, but it is difficult to decrease the thickness of the printed circuit board.
Therefore, an object of the present invention is to provide an ultra-thin flexible printed circuit board.
Another object of the present invention is to provide a printed circuit board having a relatively fine circuit pattern which is formed at an outer layer thereof.
Still another object of the present invention is to provide a printed circuit board in which a solder bump and an inner lead, is formed at the opposite side of an opening of a blind via hole.
Yet another object of the present invention is to provide a printed circuit in which an opening of a blind via hole is directed to the center rather than to the outer surface thereof.
Still yet another object of the present invention is to provide a printed circuit board in which a circuit pattern to be formed at the upper surface thereof is thinner than a circuit pattern to be formed at the lower surface connected to a pain printed circuit board.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a multi-layer printed circuit board on which insulation resin layers and circuit pattern layers are alternatively stacked to form multiple layers, including: an insulation resin layer; a circuit pattern formed at the upper surface of the insulation resin layer; a blind via hole formed by penetrating the insulation resin layer and the circuit pattern; a plated layer formed at the upper surface of the circuit pattern, at the inner wall face and the bottom of the via hole; an inner lead bump pad formed at the surface of the plated layer which is exposed to the lower surface of the insulation resin layer; and an outer lead bump pad formed on the circuit pattern which is formed at the upper surface of the insulation resin layer.
To achieve the above objects, in the multi-layer printed circuit board of the present invention, a solder resist layer is filled in the blind via hole.
To achieve the above objects, in the multi-layer printed circuit board of the present invention, the inner lead bump pad is formed at the center of the blind via hole.
To achieve the above objects, there is provided a multi-layer printed circuit board including: a first substrate having a plurality of stacked resin layers, circuit patterns formed at the upper surface of each resin layer, blind via holes formed between the circuit patterns and plated layers formed at the inner wall face of the blind via holes and at the upper surface of the circuit patterns; and a second substrate having a plurality of stacked resin layers, circuit patterns formed at the upper surface of each resin layer, blind via holes formed between the circuit patterns and plated layers formed at the inner wall face of the blind via holes and at the upper surface of the circuit patterns, wherein the blind via hole of the first substrate and the blind via hole of the second substrate are disposed to face each other.
To achieve the above objects, in the multi-layer printed circuit board of the present invention, a core resin layer is formed between the first substrate and the second substrate for attaching the two substrates together.
To achieve the above objects, the multi-layer printed circuit board of the present invention further includes a through hole vertically penetrating the first substrate, the second substrate and the core resin layer. A substrate connecting plated layer is formed at the inner wall of the through hole.
To achieve the above objects, the first substrate of a multi-layer printed circuit board of the present invention includes: a first resin layer; a first circuit pattern formed at the upper surface of the first resin layer; a first blind via hole formed penetrating the first resin layer and the first circuit pattern; a first plated layer formed at the upper surface of the first circuit pattern and at the inner wall face and the bottom of the first blind via hole; a second resin layer formed at the upper surface of the first plated layer and the first resin layer; a second circuit pattern formed at the upper surface of the second resin layer; a second blind via hole formed penetrating the second circuit pattern and the second resin layer; a second plated layer formed at the upper surface of the second circuit pattern and at the inner wall face and the bottom of the second blind via hole; and a third circuit pattern formed at the surface of the first plated layer which is exposed to the first resin layer, wherein a core resin layer is filled in the second blind via hole.
To achieve the above objects, there is also provided a BGA semiconductor package including: a multi-layer printed circuit board having an insulation resin layer, circuit patterns formed at the upper surface of the insulation resin layer, a blind via hole formed penetrating the insulation resin layer and the circuit patterns, a plated layer formed at the upper surface of the circuit pattern and at the inner wall face and the bottom of the via hole, an inner lead bump pad formed at the surface of the plated layer exposed to the lower surface portion of the insulation resin layer, and an outer lead bump pad formed on the circuit pattern formed at the upper surface of the insulation resin layer; an inner lead bump attached on the surface of the inner lead bump pad; a semiconductor chip attached at the inner lead bump; and an outer lead bump attached on the surface of the outer lead bump pad.
To achieve the above objects, there is also provided a method for fabricating a multi-layer printed circuit board including the steps of: positioning a splitting member at one face of a core forming resin layer; stacking a first metal thin layer and a first insulation resin layer at one face of the splitting member and of the core forming resin layer; etching the first insulation resin layer to expose the first metal thin layer, to thereby form a first blind via hole; forming a first circuit pattern at the upper surface of the first insulation resin layer; forming a first plated layer at the upper surface of the first circuit pattern, at the inner wall face of the first blind via hole and at the upper surface of the first metal thin layer; sequentially stacking a second insulation resin layer and a second metal thin layer at the upper surface of the first insulation resin layer and of the first plated layer; etching the second insulation resin layer and the second metal thin layer to expose the upper surface of the first plated layer, to thereby form a second blind via hole; forming a second plated layer at the upper surface of the second metal thin layer and at the inner wall face and the bottom of the second blind via hole; patterning the second metal thin layer to form a second circuit pattern; separating the core forming resin layer and the splitting member from the first metal thin layer; and patterning the first metal thin layer to form an inner lead bumping pad.
To achieve the above objects, the method for fabricating a multi-layer printed circuit of the present invention further includes the steps of: forming an outer lead bumping pad at the upper surface of the second plated layer; attaching the outer lead bump at the upper surface of the outer lead bumping pad; and attaching the inner lead bump to the upper surface of the inner lead bumping pad.
To achieve the above objects, there is also provided a method for fabricating a multi-layer printed circuit board including the steps of: positioning a splitting member having a smaller size than the core forming resin layer on one face of the core forming resin layer, sequentially stacking the first thin metal plate having a greater size than the splitting member, the first insulation resin and the second thin metal plate on the splitting member, and attaching the core forming resin, the first insulation resin or the first thin metal plate; forming a blind via hole penetrating the first insulation resin layer and the second thin metal plate; forming a conductive layer at the first thin metal plate, the second thin metal plate and the inner wall face of the blind via hole to electrically connect the first thin metal plate and the second thin metal plate; patterning the second thin metal plate and the conductive layer to form a circuit pattern; removing the core forming resin layer and the splitting member; and patterning the first thin metal plate separated from the splitting member and forming inner lead bumping pads, at least one inner lead bumping pad being formed at the bottom of the blind via hole.
To achieve the above objects, the method for fabricating a multi-layer printed circuit board further includes the step of forming an outer lead bumping pad at the upper surface of the circuit pattern.
To achieve the above objects, the method for fabricating a multi-layer printed circuit board further includes the steps of forming an inner lead bump at the upper surface of the inner lead bumping pad; and forming an outer lead bump at the upper surface of the outer lead bumping pad.
To achieve the above objects, there is also provided a method for fabricating a multi-layer printed circuit board including the steps of: positioning a splitting member having a smaller size than the core forming resin layer on both faces of the core forming resin layer, sequentially stacking the first thin metal plate having a greater size than the splitting member, the first insulation resin and the second thin metal plate on the upper surface of each splitting member, and attaching the core forming resin, the first insulation resin or the first thin metal plate; forming a blind via hole by penetrating the first insulation resin layer and the second thin metal plate; forming a conductive layer at the first thin metal plate, the second thin metal plate and the inner wall face of the blind via hole to electrically connect the first thin metal plate and the second thin metal plate; patterning the second thin metal plate and the conductive layer to form a circuit pattern; removing the core forming resin layer and the splitting member to separate the structures formed at both faces of the core forming resin layer to divide into a first substrate and a second substrate; and patterning the first substrate and the first thin metal plate to form inner lead pumping pads, at least one inner lead bumping pad being formed at the bottom of the blind via hole.
To achieve the above objects, the method for fabricating a multi-layer printed circuit board of the present invention includes the steps of; disposing the openings of each blind via hole of the first and the second substrates to face each other, disposing a core resin between the first and the second substrates, and attaching the first and the second substrates; and patterning the first thin metal plate of the first substrate to form an inner lead bumping pad and patterning the first thin metal plate of the second substrate to form an outer lead bumping pad, after the step of dividing into the first and the second substrates.
To achieve the above objects, the method for fabricating a multi-layer printed circuit board further includes the steps of: forming a through hole penetrating the first substrate, the second substrate and the core forming resin; and forming a conductive layer at the inside of the through hole and at the upper surface of the inner lead bumping pad and of the outer lead bumping pad, before forming the inner lead bumping pad and the outer lead bumping pad.